Noise Criteria
Reference data and engineering information about noise criteria for acoustics applications.
Overview
Engineering reference data for Noise Criteria in acoustics.
Key Formulas
Speed of Sound
Speed of sound in an ideal gas.
Sound Level
Decibel level.
Wavelength
Wavelength = speed / frequency.
Variables
| Symbol | Description | Unit |
|---|---|---|
| Speed of sound | m/s | |
| Sound level | dB | |
| Wavelength | m | |
| Frequency | Hz |
Type of Room - Occupancy | Maximum Level (dB) | Noise Criterion (NC, NCB, RNC) | Noise Rating (NR) | dB(A) | Room Criteria (RC) |
|---|---|---|---|---|---|
| Very quiet (Concert halls, recording studios, theaters, etc.) | 10 - 20 | 20 | 20 | 25 - 30 | 20 |
| Quiet (Private bedrooms, live theaters, studios, conference rooms, libraries, etc.) | 20 - 25 | 25 | 25 | 25 - 30 | 25 |
| Moderate (Private living rooms, board rooms, hotel bedrooms) | 30 - 40 | 30 | 30 | 30 - 35 | 30 |
| Moderate noisy (Public hotel rooms, small offices, classrooms, courtrooms) | 30 - 40 | 35 | 35 | 40 - 45 | — |
| Noisy (Drawing offices, toilets, bathrooms, lobbies, department stores, etc.) | 35 - 45 | 40 | 40 | 45 - 55 | 40 |
| Very noisy (Kitchens, laundry rooms, computer rooms, canteens, supermarkets, etc.) | 40 - 50 | 45 | 45 | 45 - 55 | 45 |
Source: engineeringtoolbox.com
Sound Pressure Level in dB(A)
The dB(A) scale, or A-weighted sound pressure level (), is a single-number rating that approximates the relative loudness perceived by the human ear. It is derived by applying a specific frequency-weighting curve (the A-weighting network) to the measured sound spectrum, which attenuates low and very high frequencies to reflect human hearing sensitivity.
This makes dB(A) a practical and widely used metric for assessing environmental and industrial noise. It is commonly specified in noise ordinances and equipment ratings, but it does not provide the same frequency-specific detail as spectrum-based criteria like NC or NR.